Swift — Syntax

Variables and constants

// let: constant (immutable)
let name = "Alice"
let age = 30

// var: variable (mutable)
var count = 0
count += 1

// Type annotation
let pi: Double = 3.14
var isActive: Bool = true

Type inference

let x = 42          // Int
let y = 3.14        // Double
let s = "hello"     // String
let b = true        // Bool

// Explicit type when needed
let price: Float = 9.99

String interpolation

let name = "Alice"
let age = 30
print("Name: \(name), Age: \(age)")
print("Next year: \(age + 1)")

Functions

// Basic function
func add(a: Int, b: Int) -> Int {
    return a + b
}

// Single expression
func multiply(a: Int, b: Int) -> Int {
    a * b
}

// Default parameters
func greet(name: String, greeting: String = "Hello") {
    print("\(greeting), \(name)!")
}

// Named arguments
greet(name: "Alice")
greet(name: "Bob", greeting: "Hi")

Control flow

// if/else
let x = 10
if x > 5 {
    print("big")
} else {
    print("small")
}

// switch
let day = "Monday"
switch day {
case "Monday":
    print("Start of week")
case "Friday":
    print("Almost weekend")
case "Saturday", "Sunday":
    print("Weekend!")
default:
    print("Midweek")
}

// for loop
for i in 1...5 {
    print(i)
}

// while
var y = 0
while y < 5 {
    y += 1
}

Optionals

var name: String? = nil

// Safe unwrapping
if let name = name {
    print(name)
} else {
    print("No name")
}

// Guard
func process(name: String?) {
    guard let name = name else {
        print("No name")
        return
    }
    print("Processing: \(name)")
}

// Nil coalescing
let display = name ?? "Unknown"

Collections

// Array
let nums = [1, 2, 3, 4, 5]
var mutable = [1, 2, 3]
mutable.append(4)

// Dictionary
let ages = ["Alice": 30, "Bob": 25]

// Set
let set: Set = [1, 2, 3, 2, 1] // [1, 2, 3]

Mini Practice

Write Swift code that:

1. Uses let and var with type inference
2. Creates a function with default parameters
3. Uses optionals with if let
4. Demonstrates a switch statement

Up Next

In the next lesson, you'll learn about Variables — declarations and types in Swift.